1. Field of the Invention
The present invention relates to a method for manufacturing a Liquid Crystal Display (LCD) and, more particularly to, a method for manufacturing the LCD in which a columnar spacer is provided to maintain a gap to be filled with liquid crystal between a driver element substrate and a facing substrate.
The present application claims priority of Japanese Patent Application No. 2001-140776 filed on May 10, 2001, which is hereby incorporated by reference.
2. Description of the Related Art
A Liquid Crystal Display (LCD) is widely used as a display for use in a variety of information apparatuses or a like The LCD has a basic configuration in that a gap is filled with liquid crystal between a TFT (Thin Film Transistor) substrate (driver element substrate) on which a Thin Film Transistor (TFT) operating as a driver element (switching element) is formed and a CF (Color Filter) substrate (facing substrate) on which a Color Filter (CF) is formed. In this configuration, conventionally, to maintain the gap between the TFT substrate and the CF substrate, a spherical spacers are disposed between these two substrates.
First, as shown in FIG. 9A, on either one of the two substrates, shown as an example, a TFT substrate 101 are distributed spherical spacers 102 prepared beforehand that are made of resin or a like and that have a diameter of 4-8 xcexcm Then, as shown in FIG. 9B, a CF substrate 103 is superposed over the TFT substrate 101 in such a manner as to come in contact with the spherical spacers 102, so that these two substrates are adhered to each other to thereby form a liquid crystal cell. In this case, the TFT substrate 101 and the CF substrate 103 are supposed to have been mounted with necessary components (elements) such as TFTs and CFs (they are not shown in the drawing for simplification) formed thereon already. Then, liquid crystal (not shown) is injected between the TFT substrate 101 and the CF substrate 103 of the liquid crystal cell, to which is then connected a peripheral driver circuit (not shown), thus completing the LCD.
Thus, according to the method for manufacturing the LCD using spherical spacers 102, as mentioned above, the spherical spacers 102 only need to be distributed on said either one of the two substrates, that is the TET substrate 101, thus giving a merit of a simplified step of providing the spherical spacers 102. Oppositely, however, by this method, the spherical spacers 102 are distributed randomly on the TFT substrate 101, so that they are not uniform in dispersion density (disposition density) and, because of their spherical shape, are liable to roll (move) on the TFT substrate 101 during manufacture, thus giving a problem that they may readily move around to thereby deteriorate a so-called an xe2x80x9con-the-surface uniformityxe2x80x9d Also, the spherical spacers 102 are present in some display picture elements, thus inevitably deteriorating contrast of the LCD.
To solve these problems, a recent LCD has, in place of the spherical spacers 102, columnar spacers disposed between the TFT substrate 101 and the CF substrate 103. For example, Japanese Patent Application Laid-open No. Hei 11-305239 discloses an LCD (shown in FIGS. 11A to 11B) having such a configuration that columnar spacers 105 are disposed between the TFT substrate 101 and the CF substrate 103. These columnar spacers 105 are typically formed on the CF substrate 103 by using the same material as the color filter and at the same time as, for example, this color filter is formed
The following will roughly describe a method for manufacturing a conventional LCD employing the columnar spacer 105 with reference to FIGS. 10A to 10D First, as shown in FIG. 10A, a photo-resist film 104 mainly made up of an acrylic resin is coated on such a surface of, for example, the CF substrate 103 on which necessary components are formed beforehand as to face the TFT substrate 101 and then exposed, developed, and patterned to form the columnar spacers 105. The columnar spacers 105 are thus formed as fixed on the CF substrate 103. The columnar spacers 105, therefore, do not vary in disposition density like the spherical spacers 102 nor move around on the CF substrate 103 when manufactured, thus avoiding deteriorating the on-the-surface uniformity. Moreover, the columnar spacers 105 can be disposed at an arbitrary position and 50 be adjusted not to be present in a display picture element, thus giving a merit of avoiding deteriorating the contrast.
Next, as shown in FIG. 10B, an oriented film 106 made up of, for example, polyimide with a solvent added is formed throughout on the CF substrate 103 by printing. Then, to remove the solvent from the inside of the oriented film 106, orientation baking processing is performed on the CF substrate 103
Then, a seal 107 made up of, for example, epoxy-resin is formed by printing at a predetermined position of the oriented film 106. In the side surface of the seal 107 is formed an injection hole 109 for injecting liquid crystal therethrough.,
On the other hand, as shown in FIG. 10C, the TFT substrate 101 on which necessary components including TFTs are formed beforehand is superposed over the CF substrate 103 in such a manner as to be in contact with the columnar spacers 105. In this superposition, the TFT substrate 101 is aligned by, specifically, shifting the TFT substrate 101 laterally with respect to the columnar spacers 105 so as to give a predetermined positional relationship between the TFT substrate 101 and the CF substrate 103 by applying a predetermined superposing load W1 on the TFT substrate 101 and the CF substrate 103. Conventional superposition values are roughly the same as those when the spherical spacer 102 is employed, where they are aligned with each other by crushing the seal 107 when applying the superposing load W1 of 0.3-0.6 kg/cm2. Then, seal baking processing is performed by heating the seal 107 to harden the columnar spacers 105 while applying seal baking load W2 (not shown) or about 0.5 kg/cm2, which is roughly the same value as that by use of spherical spacers 102, across these the TFT substrate 101 and the CF substrate 103 thus superposed one over the other. By doing so, a gap 108 is maintained between the TFT substrate 101 and the CF substrate 103 due to the columnar spacers 105, thus forming a liquid crystal cell.
Next, as shown in FIG. 10D, liquid crystal 110 is injected through the injection hole 109 in the seal 107 to then perform under-pressure hole sealing processing for determining the gap 108 finally. This under-pressure hole sealing is carried out specifically by expelling extra liquid crystal from the inside of the liquid crystal cell and also as applying an under-pressure hole sealing load W3 of at least about 0.6 kg/cm2 to make the gap 108 uniform. Subsequently, a peripheral driver circuit (not shown) is connected to the liquid crystal cell, thus completing the LCD.
This conventional method for manufacturing the LCD, however, has a problem that it is difficult to form a stable gap 108 using columnar spacers 105 because these columnar spacers 105 are affected by the heat or the load from the manufacturing process after they are formed.
First, after being formed, the columnar spacers 105 shrink owing to the heat produced by the processing of an orientation baking process, thus being decreased in height. As shown in FIG. 11A, when the columnar spacers 105 are formed on the CF substrate 103 and the oriented film 106 is printed throughout the surface and then the orientation baking processing is performed, the resultant heat affects the columnar spacers 105 so that they would be fixed as shrunk as shown in FIG. 11B, thus the gap 108 formed between them and the TFT substrate 101 narrowing.
Also, although in the under-pressure hole sealing process to determine the gap 108 finally, in order to make the gap 108 uniform, preferably a large under-pressure hole sealing load is applied to expel the extra liquid crystal 110, this large under-pressure hole sealing load has such an influence that when the temperature of an environment in which the LCD is used is changed, the shrinkage of the columnar spacers 105 cannot keep pace with the shrinkage of the volume of the liquid crystal 110. As shown in FIG. 12A, if the large under-pressure hole sealing load W3 (for example, 0.6 kg/cm2) is applied in under-pressure hole sealing, the columnar spacers 105 are compressed. If, in this case, the columnar spacers 105 are sufficiently compressed already as shown in FIG. 12A, they can keep pace in expansion with the liquid crystal 110 even when the environmental temperature is raised (to, for example, 70-80xc2x0 C.), thus maintaining a uniform gap 108. If the liquid crystal 110 expands more than this preceding compression degree of the columnar spacers 105, however, as shown in FIG. 12B, the columnar spacers 105 cannot keep pace in expansion with the liquid crystal 110 in an arrow direction and so are separated from the TFT substrate 101, thus making it impossible to maintain a uniform gap.
In a case where the environmental temperature is lowered (to, for example, xe2x88x9210xc2x0 C. through xe2x88x9220xc2x0 C.), on the other hand, when the columnar spacers 105 are sufficiently compressed already as mentioned above and if the liquid crystal 110 shrinks in the arrow direction as shown in FIG. 12C, the columnar spacers 105 cannot be compressed any more and so cannot keep pace with the liquid crystal 110 in shrinkage. As a result, a gas contained in the liquid crystal 110 gives rise to air bubbles 111, which in turn deteriorates transmittance of light.
If the large under-pressure hole sealing load is thus applied to seal the hole under pressure, the columnar spacers 105 cannot keep pace with the liquid crystal 110 in expansion or shrinkage when the environment in which a finished LCD is used is exposed to a temperature which is higher or lower than the ordinary (room) temperature respectively, thus making it difficult to form a uniform gap
Also, by the conventional method for manufacturing the LCD, the columnar spacers 105 are affected by the heat or pressure applied in the manufacturing process after they are formed, thus making it difficult to manufacture a high-quality LCD.
That is, if the TFT substrate 101 and the CF substrate 103 are superposed one over the other while applying the large superposing load in the superposing process, they cannot easily be aligned with each other. If, as shown in FIG. 13A, the TFT substrate 101 is disposed and then, as shown in FIG. 13B, the large superposing load W1 (of, for example, 0.3-0.6 kg/cm2) is applied thereon, resultantly the TFT substrate 101 has a large friction force against the columnar spacers 105 on the CF substrate 103. This makes it difficult to shift the TFT substrate 101 laterally, which in turn makes it difficult to align these substrates (TFT substrate 101 and CF substrate 103) with each other, so that if the TFT substrate 101 is forcedly slipped, its surface may be damaged by the columnar spacers 105, thus possibly deteriorating the TFTS, the oriented film 106, or a like formed on that surface The deterioration, therefore, decreases the manufacture yield of the LCD, thus making it difficult to consistently manufacture a high-quality LCD.
Also, since the seal baking process following the superposing process involves not only pressure application due to seal baking load but also heating, resultantly the columnar spacers may be deformed readily. The columnar spacers 105 before seal baking such as shown in FIG. 14A, are subject to a drop in hardness in seal baking owing to application of the seal baking load W2 and the heat as shown in FIG. 14B and so readily deformed, thus being left as deformed even after seal baking as shown in FIG. 14C. In this case also, a uniform gap cannot be maintained
In view of the above, it is an object of the present invention to provide an LCD manufacturing method that can form a stable gap using columnar spacers and also that can manufacture a high-quality LCD.
According to a first aspect of the present invention, there is provided a method for manufacturing an LCD including a driver element substrate on which a driver element is formed and a facing substrate which faces the driver element substrate, into a gap between which is injected liquid crystal, a columnar spacer for maintaining the gap being disposed between the driver element substrate and the facing substrate, including;
a columnar spacer forming step for forming the columnar spacer on either one of the driver element substrate and the facing substrate;
a seal forming step for forming a seal for adhering the driver element substrate and the facing substrate to each other after the columnar spacer is formed;
a liquid crystal injecting step for injecting the liquid crystal through an injection hole formed in the seal beforehand after the driver element substrate and the facing substrate are adhered to each other by the seal; and
an under-pressure hole sealing step for sealing the injection hole after an extra amount of the liquid crystal is expelled through the injection hole, to then apply an under-pressure hole sealing load value of 0.15-0.60 kg/cm2 across the driver element substrate and the facing substrate in order to determine the gap finally.
In the foregoing, a preferable mode is one wherein between the seal forming step and the liquid crystal injecting step is interposed a superposing step for applying a superposing load value of 0.03-0.12 kg/cm2 across the driver element substrate and the facing substrate to crush the seal in order to adhere the driver element substrate and the facing substrate to each other.
Another preferable mode is one wherein the superposing step is followed by a seal baking step for baking the seal by applying across the driver element substrate and the facing substrate a seal baking load value less than the under-pressure hole sealing load value employed in the under-pressure hole sealing step.
Still another preferable mode is one wherein the columnar spacer forming step is followed by an oriented film forming step for forming an oriented film to cover the columnar spacer.
Further preferable mode is one wherein the oriented film forming step is followed by an oriented film baking step for baking the oriented film to remove a sol vent therefrom.
Still further preferable mode is one wherein the oriented film baking step is performed at a temperature of 150-230xc2x0 C. for one to three hours.
An additional preferable mode is one wherein the columnar spacer forming step is performed by applying a photo-resist film on said either one of the driver element substrate or the facing substrate to then pattern the photo-resist film into a desired shape.
Still additional preferable mode is one wherein the photo-resist film employed is of a negative type.
Further preferable mode is one wherein the columnar spacer is formed in a light-blocking region.
Still further position of the light-blocking region is selected in a region where a black matrix layer is formed.
With the above configurations, the columnar spacer is formed for maintaining the gap between the driver element substrate and the facing substrate to be filled with the liquid crystal to then perform the under-pressure hole sealing processing which determines the gap finally at the under-pressure hole sealing load value of 0.15-0.60 kg/cm2, so that even when an environment in which a finished LCD is used is exposed to a high or low temperature other than a ordinary (room) temperature, the columnar spacer can keep pace with the liquid crystal in expansion and shrinkage, thus making it to form a uniform gap.
Therefore, it is possible to form a stable gap by use of the columnar spacer and also to manufacture a high-quality LCD.